Oil or fat lipids possess high caloric contents (9 kcal/g) and thereby food intake containing high quantities of these lipids can promote obesity and other life-style related diseases.
Research so far has been mainly directed to the study of fatty acids constituting a triglyceride, a principal component of a lipid. Nutritionally essential fatty acids are, for example, linoleic acid, arachidonic acid and linolenic acid. These fatty acids are known to be utilized in the body as a constituent of a biomembrane or a raw material of eicosanoids (prostaglandin, thromboxanes, leukotrienes, etc.). In addition, it is reported that there is a high possibility that a diet high in saturated fatty acids can lead to increases in the blood-serum cholesterol level, leading to atherosclerosis or heart disease (Lancet, 2, 959(1950)); and that high levels of linoleic acid oil in the diet increases tumor incidence and size in experimental animals (J. National Cancer Institute, 66, 517(1971)). It is reported that an oleic-acid-rich and saturated-fatty-acid poor diet will lower LDL-cholesterol levels, while maintaining HDL-cholesterol levels, thereby reducing the risk of heart diseases (J. Lipid Res., 26, 194(1985), New England J. Medicine, 314, 745(1988)). In addition, the physiological activity of various ω 3-unsaturated fatty acids, including antithrombus effects of eicosapentaenoic acid, contained in fish oil has drawn attention (Ann. Rev. Nutr., 8, 517(1988)). However, owing to the high degree of unsaturation of eicosapentaenoic acid and docosahexaenoic acid, these compounds have reduced stability to oxidation; and eicosapentaenoic acid is a known anticoagulant. Based on a study of the intake balance of these fatty acids, research reports recommend a ratio of saturated fatty acids: mono-unsaturated fatty acid polyunsaturated fatty acid or a ratio of ω 6-unsaturated fatty acid: ω 3-unsaturated fatty acid. Research in this area is still in progress (“Nutrition and Diseases of Oils and Fats”, published by Saiwai Shobo, “The 6th edition of Recommended Dietary Allowances for Japanese, Ministry of Health and Welfare”).
With a view to preventing obesity, substitutes for fats and oils or non-absorptive fats and oils have been developed and typical ones include sucrose fatty acid polyester (U.S. Pat. No. 3,600,186) which can be excreted without being absorbed into the body so that the calories derived from such a fat is essentially 0 kcal/g. There is, however, the potential problem that these fats can result in anal leakage and also may inhibit absorption of fat-soluble vitamins. Moreover, these fats do not have food value as an essential fatty acid. Nevertheless, the use of these fats have been authorized by the FDA in 1996, with the restriction that semi-solid or solid sucrose fatty acid polyesters, having a melting point of 37.8 to 71.1° C. and containing predetermined amounts of vitamins A, D, E and K, may be used only for salty snack foods.
It is also known that medium-chain fatty acid triglycerides (MCT) are not accumulated in the body, but possess poor heat stability. Similar effects have been disclosed for conjugated linoleic acid, fish oil or perilla oil (Lipids, 32, 853(1997), J. Agric. Food Chem., 46, 1225(1998)).
One recent study reported an agent containing a glyceride structure for lowering the triglyceride concentration in serum (Japanese Patent Application Laid-Open No. 5-310567), but this study focused only on the structure of monoglycerides and did not report effects of monoglycerides at maximum concentrations.
The use of polyunsaturated-fatty-acid-containing oil/fat powders (Japanese Patent Application Laid-Open No. 6-172782), polyunsaturated-fatty-acid-containing oil/fat compositions and polyunsaturated-fatty-acid-containing aqueous foods (Japanese Patent Application Laid-Open No. 7-39302), have been disclosed wherein their dispersibility in water is improved by adoption of a polyunsaturated fatty acid having a monoglyceride structure. These reports, however, only refer generally to physiological effects. One fish-oil-monoglyceride used in the above-described composition has a very unfavorable taste, is apt to become solid on storage, has a rough mouth feel, must be dissolved by heat for use and is low in linoleic acid, one of the essential fatty acids.
Accordingly, the object of the present invention is to provide an extremely useful oil/fat composition which has excellent processing properties, is safe, pleasant tasting, has hepatic function improving action, body-fat burning action, and is healthy.